> ## Documentation Index
> Fetch the complete documentation index at: https://docs.gradium.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# API Reference

> Gradium API endpoints for Text-to-Speech, Speech-to-Text, Voices, Pronunciations, and Metering

## Welcome

The Gradium API provides low-latency, high-quality Text-to-Speech and Speech-to-Text capabilities. This reference documents all available REST and WebSocket endpoints.

<Card title="OpenAPI Specification" icon="file-code" href="/api-reference/openapi.json">
  Download the OpenAPI specification file
</Card>

## Authentication

All API endpoints are authenticated using an API key passed via the `x-api-key` header:

```bash theme={null}
x-api-key: your_api_key
```

## Server URL

Use the following base URL for all REST endpoints:

```
https://api.gradium.ai/api
```

For WebSocket endpoints, use:

```
wss://api.gradium.ai/api
```